It is common practice to transform an array of black/white picture elements of a facsimile image into a more compact or compressed form to reduce the number of binary bits that must be stored or transmitted. Many compression techniques operate to substitute code words for linear segments of binary picture elements. One common technique, known as run length coding, encodes successive alternate colored line segments by a code word indicating the number of picture elements of one color in each segment. A more complex technique supplements the run length coding, where efficient, by encoding some line segments by reference to color transitions occurring on a preceding or reference line.